Continuously adjustable contactless potentiometer



1966 H. HIERONYMUS 3,267,404

CONTINUOUSLY ADJUSTABLE CONTACTLESS POTENTIOMETER Filed March 11, 1964 5Sheets-Sheet 1 5 1 -E-f-a u U O 0 Fig.1 Fig. 2 Flg. 3

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United States Patent 3,267,404 CONTINUQUSLY ADJUSTABLE CONTACTLESSPQTENTIDMETER Hans Hieronymus, Erlangen, Germany, assignor toSiemens-Schucirertwerke Alrtiengeselischaft, Berlin- Siemensstadt,Germany, a corporation of Germany Filed Mar. 11, 1964, Ser. No. 350,974Claims priority, application Germany, Mar. 13, 1963,

17 Ciaims. (Cl. 338-32 My invention relates to potentiometers whoseresistance bodies consist of semiconductor material and greatly varytheir electric resistance under the effect of a magnetic field. Suchgalvanomagnetic resistors are known from US. Patent 2,894,234 of H.Weiss and H. Welker, assigned to the assignee of the present invention.Among the known resistors of this kind are so-called field plates ofindium antimonide (InSb). When, for example, such a plate is subjectedto a magnetic field of 10,000 gauss, the ohmic resistance of the platechanges to a value to times larger than the resistance at zero field,

Referring to such galvanomagnetic resistors, it is an object of myinvention to provide a potentiometer whose voltage dividing circuit isentirely free of mechanical contacts and which affords a fullycontinuous adjustment of the output voltage.

Another object of the invention is to devise a continuously adjustablepotentiometer which possess a virtually unlimited lifetime, free of anywear, regardless of the frequency of its use within the rated limits ofits electrical rating, and which exhibits a substantially logarithmicalresistance characteristic without the aid of any additional circuitcomponents.

Still another object of my invention is to devise a potentiometer that,by virtue of an extremely small inherent capacitance, is particularlywell suitable for dividing alternating voltages of high frequency.

A further object of my inVentiOnis to provide a continuously adjustablepotentiometer which, in addition to meeting one or more of theaforestated objects, permits obtaining any desired high ratio of voltagedivision.

According to my invention, I connect two galvanomagnetic resistancemembers in series with each other so as to form a voltage dividercircuit with an intermediate tap, and I dispose the two members in thefield of a magnetic field structure so that the respective resistancevalues are dependent upon the magnetic flux traversing the two members.Furthermore, I mount the two galvanomagnetic resistance members in fixedrelation to each other in respectively different positions relative tothe magnetic field structure, and provide the device with continuouslyadjustable means for inversely controlling the amounts of magnetic fluxthrough the respective members, so that increased flux through onemember coincides with decreased flux in the other.

According to another feature of my invention, the two galvanomagneticresistance members of the voltage divider circuit are mounted on acarrier structure at respectively different locations, and the carrierstructure with the attached resistance members is displaceable withrespect to the magnetic field structure, or vice versa, to therebyprovide for the above-mentioned inverse control of the respectivelyincreasing and decreasing amounts of mag netic flux passing through thetwo members.

According to still another feature of my invention, the twogalvanomagnetic resistance members consist of flat bodies and aremounted on a carrier structure of elongated prismatic shape, namely ondifferent lateral prism surfaces extending at a right angle to eachother, the carrier structure or field structure being rotationallyadjustable about the longitudinal axis of the carrier structure forvarying the magnetic flux to increase in one member as it decreases inthe other.

According to a further feature of my invention, I provide at least oneadditional pair of serially interconnected galvanomagnetic resistancemembers, and electrically connect each such pair in parallel relation toone of the galvanomagnetic resistance members in a preceding voltagedivider circuit, the resistance members of all pairs thus interconnectedbeing distributed over the above-mentioned two different localities orsurfaces of the carrier structure so that, during a change inpotentiometric adjustment, the magnetic flux through one group ofgalvanomagnetic members increases while the flux in the other groupdecreases.

' According to still another feature of my invention, the twogalvanomagnetic resistance members of the abovementioned voltage dividercircuit or circuits are located in respective field gaps of the twoouter legs formed by a three-legged magnetizable core whose center legcomprises magnetizing means for passing magnetic flux through both fieldgaps, and which is provided with control winding means to superimposeupon the outer legs another magnetic flux, thus boosting the fieldintensity in one gap and reducing it in the other.

The invention will be further described with reference to embodiments ofpotentiometers according to the invention illustrated by way of exampleon the accompanying drawings in which:

FIG. 1 shows schematically a potentiometer device having a generally C-or O-shaped magnet in whose gap a galvanomagnetic assembly isrotationally adjustable.

FIGS. 2 and 3 are respectively different circuit diagrams ofgalvanomagnetic resistors applicable in a device according to FIG. 1.

FIG. 4 is a schematic and perspective view of the galvanomagneticassembly accord-ing to FIGS. 1 and 3.

FIG. 5 shows another modification of a potentiometer circuit applicablefor the purposes of the invention.

FIG. 6 is a planar development of a carrier structure equipped withgalvanomagnetic resistor members; and FIG. 7 is a perspective view of asimilar, but somewhat modified assembly.

FIG. 8 is a partial view of another embodiment, also comprising arotationally adjustable galvanomagnetic resistor assembly.

FIG. 9 shows schematically a galvanomagnetic potentiometer which isadjustable by means of a translatory motion, FIG. 9a shows a similarmodification, and FIG. 10 illustrates a control mechanism for impartingsuch motion to the assembly.

FIG. 11 shows a galvanomagnetic potentiometer according to the inventionoperating without any movable parts.

FIGS. 12 and 13 are explanatory graphs relating to invention.

The potentiometer device shown in FIG. 1 comprises a carrier structure 1for a plate-shaped resistance member. The carrier 1 is rotationallyadjustable about an axis A-B and is located in an air gap of a permanentmagnet 2. When the resistance carrier 1 or the magnet 2 is rotated aboutthe .axis A-B to a different angular position, the magnetic fluxtraversing the resistance members on the carrier 1 changes, each memberthen exhibiting a diiferent resistance value depending upon the relativeposition of that member to the permanent magnet 2. As mentioned, theresistance members used for this purpose consist preferably of indiumantimonide or indium arsenide, although other semiconductor substancesare also applicable. In

this respect reference may be had to the above-mentioned patent.

FIG. 2 shows the simplest form of an applicable voltage divider circuitcomprising only two galvanomagnetic resistance members 3 and 4. Theinput voltage -U is impressed across a series connection of the twomembers. The continuously variable 'output voltage U; is tapped off theterminals of resistance member 4. The two resistance members have theform of flat plates (field plates). Their planes are perpendicular toeach other in the air gap of the magnet 2. Preferably, the two platesare cemented to respective mutually perpendicular surfaces of aprismatic rod having a rectangular or preferably square cross section,corresponding to the insulating carrier structure 1 shown in FIG. 4.When rotating the rod-shaped carrier about its longitudinal axis A-Cwhich is parallel to the surfaces upon which the field plates areattached and which is also perpendicular to the direction of themagnetic flux in the air gap of the permanent magnet 2, the resistanceof one field plate increases and the resistance of the other field platesimultaneously decreases. With such a galvanomagnetic assembly, aconsiderable ratio of voltage division can already be achieved, thisratio denoting the relation of the highest to the lowest attainableoutput voltage.

The division ratio depends upon the ratio n of the respective baseresistances exhibited by the two galvanomagnetic plates employed when nomagnetic field is eifective. This will be further explained withreference to the graph shown in FIG. 12 where the abscissa denotes thebase-resistance ratio It (on a linear scale) and the ordinate indicatesrelative output voltages (on a logarithmic scale). The dot-and-dashcurve U /U represents the lowest output voltage U relative to the inputvoltage U in dependence upon the base-resistance ratio n, relating to aresistance assembly according to FIGS. 1 and 2 in which a rotationalchange of 90 results in a resistance change by the factor 10. Thebroken-line curve U' /U represents the ratio of the highest adjustableoutput voltage to the input voltage U likewise as a function of the baseratio n which is always somewhat smaller than unity. The full-line curveU /U shows the ratio of the lowest to the highest adjustable outputvoltage, likewise in dependence upon the ratio n of the baseresistances. It will be recognized, for example, that at the value n=3,the output voltage can be varied in the ratio of 1:25. At thatoutput-voltage ratio, the highest output voltage U amounts to 80% of theinput voltage. From then on, the gain in attainable voltage-divisionratio increases only little with increasing 11, whereas the highestpossible value of output voltage still continues to decreaseconsiderably.

If the ratio of the output voltage U to the attainable maximum of outputvolt-age U; is plotted over the rotational angle of the square carrier1, the curve I shown in the graph of FIG. 13 is obtained, based upon thebase ratio n=3. In FIG. 13 the abscissa denotes the angle of rotationaladjustment (linear scale) and the ordinate indicates output voltage(logarithmic scale).

A further increase in voltage-division ratio is obtained by multiplevoltage division. Thus, FIG. 3 shows an applicable divider circuit witha double division. The galvanomagnetic members 3 and 4 are connected andmounted in the same manner as described above with reference to FIGS. 1and 2. Connected in parallel relation to the resistance member 4 is apair of seriesconnected galvanomagnetic resistance members '5 and 6. Theoutput voltage U appears between the terminals of member 6. The fourgalvanomagnetic members are mounted on two mutually perpendicularsurfaces of the carrier structure 1 according to FIG. 4.

The diagram in FIG. 12 also shows curves corresponding to the doublevoltage division just described, these curves being marked by the indexII. The base resistances of the galvanomagnetic members 3 and 5 arechosen to be equal and in each case are n-times larger than the baseresistances of the members 4 and 6 respectively. The curves apply to thecase that the resistance values of all four resistance members change bythe factor 10 when the assembly is turned in the magnetic field. It willbe recognized from FIG. 12 relative to the divider circuit of FIG. 3,that with a double voltage division a voltage-divider ratio of 1:500 canbe achieved, relating to a base-resistance ratio of 11:3. The highestpossible output voltage in this case is approximately 50% of the inputvoltage U Curve II in FIG. 13 indicates, for the same values, the ratioof output voltage to attainable maximum of output voltage in dependenceupon the angular position of the assembly.

As mentioned, FIG. 4 exemplifies a preferred geometrical arrangement ofthe four galvanomagnetic members 3, 4, 5 and 6. The members 3 and 5 arecemented to one surface of a rod-shaped carrier having a square crosssection, the members 4 and 6 are attached to an adjacent surface andhence extend perpendicularly to the plane of members 3 and 5. In thisembodiment the arrangement of the connecting leads between theindividual semiconductor plates is so chosen that a minimal amount ofwiring suffices and the terminals for the input and output voltages Uand U are located at the respective ends of the rod-shaped carrier. Thusthe terminals are kept spacially most remote from each other on thecarrier, which is of advantage when using the potentiometer forhigh-frequency purposes.

FIG. 12 further shows corresponding curves for potentiometer deviceswith triple and quadruple voltage division, comprising six and eightgalvanomagnetic resistors respectively. An example for a circuit witheight galvanomagnetic members is shown in FIG. 5. The members areconnected pairwise in series, and each following pair of members lies inparallel to one member of the preceding resistance pair. Thus, thegalvanomagnetic members 7 and 8 are connected in parallel to member 6,and members 9 and 10 are in parallel to member 8. The output voltage Uis taken from the terminals of member 10.

As shown in FIG. 6, the eight resistors are preferably distributeduniformly over the four lateral surfaces a, b, c, d of a squarerod-shaped carrier structure. The surfaces a and c are parallel to eachother and carry the flat field plates 3, 5, 7, 9 and consequently onemember from each of the four pairs. The other members 4, 6, 8 and 10 aremounted on the surfaces b and d extending perpendicular to the surfacesat and c. Thus, the two series-connected members of each individualpair, for example 5 and 6, are always fastened to mutually perpendicularsurfaces. As mentioned with reference to FIG. 4, the wiring is effectedin such a manner that the terminals for the input voltage U and theoutput voltage U are most remote from each other.

As will be seen from FIG. 12 for the quadruple voltage divisionaccording to FIGS. 5 and 6, the output voltage U can be varied in therange of 1: 180,000 for the base-resistance ratio 11:3.

The embodiment shown in FIG. 7 also comprises eight resistance members.However, the members 3, 5, 7 and 9 are combined to a singlesemiconductor strip which is provided with corresponding taps andmounted on a single lateral surface of the square carrier. An adjacentlateral surface of the carrier 1, perpendicular to the one firstmentioned, is provided with the other four galvanomagnetic members. Themembers 4 and 6 are combined to a single semiconductor plate which ispro vided with a mid-tap, and the members 8 and 10 are analogouslycombined to a single field plate with a midtatp. When producing theassembly, the members 4, 6, 8 and 10 are preferably made of a singlesemiconductor strip, similar in shape to that comprising the members 3,5, 7 and 9. After the single strip is cemented to the carrier 1, it isseparated between members 6 and 8 into the illustrated two parts. aremounted, in analogy to FIGS. 4 and 6, so as to provide for lowestpossible inherent capacitance ofl the assembly.

For shielding purposes, the carrier structure may also The connectingwires be made of metal or other conducting material if thegalvanomagnetic members are insulated from the carrier material. If itis desired to reduce the effective a r gap and to also decouple theindividual galvanomagnetic members with respect to alternating voltages,it is preferable to make the carrier structure of a ferromagnetic andelectrically conducting material. Thus, in the embodiment according toFIG. 8, the carrier 11 consists of an elongated rod having a squarecross section and consisting of ferromagnetic and electricallyconducting material such as magnetically soft iron, sintered iron powderor ferrite. The carrier is rotatable about its longitudinal axis betweenthe poles 12 of the permanent magnet, or vice versa. Galvanomagneticfield plates are cemented upon the four lateral surfaces of the carrier,only four such field plates being shown at 3, 4, 7 and 8 in FIG. 8,corresponding to those denoted by the same respective numerals in FIGS.5 and 6. Cemented upon the resistance members are cylindrical segments13, 14, 15 and 16 which consist likewise of ferromagnetic andelectrically conducting material. The radius of these segments is sochosen that the overall cross section, formed by the segments togetherwith the square cross section of the rod 11, is circular, thus resultingin a generally cylindrical shape of the assembly in the air gap.

In the potentiometer shown in FIG. 9, two galvanomagnetic resistanceplates 17 and 18 are fixed to each other in a plane longitudinallybeside each other. They are jointly displaceab-le in the air gap of amagnet whose pole shoes are denoted by 19 and 20. The direction ofdisplacement, indicated by a double-headed arrow, is transverse andperpendicular to the direction of the magnetic flux in the gap. The polefaces ofpole shoes 19 and 20 have substantially the same dimensions asthe areas of the resistance plates. Hence, depending upon the relativeposition between the pole shoes and the resistance plates, either plate17 or plate 18 is more or less located in the magnetic field, it beingirrelevant whether the galvanomagnetic assembly is displaced withrespect to the magnet, or the magnet is displaced relative to theassembly. I

By placing several pairs of adjoining galvanomagnetic members of thistype on top of each other, the device of the type shown in FIG. 9 canalso be employed for having a single magnet efiect a multiple voltagedivision to obtain a higher division ratio. A mutual shielding of theindividual pairs of resistance members, located closely above eachother, can be effected by interposing a metal foil.

The device shown in FIG. 9a exemplifies a modification of thejust-mentioned kind. It comp-rises a sandwich assembly of three pairs ofgalvanomagnetic resistance members 91a and b, 92a and b, 93a and b. Thezero potential is denoted by 0, the input voltage by U and the outputvoltage by U The contacts 95 serve for supplying current as well as forinterconnecting the individual resistance members. The members areinserted into the air gap between the' poles N and S of a magnet and aredisplaceable in a direction perpendicular to the lines of magneticforce, this direction being indicated :by an arrow. The pole races ofthe magnets have approximatelythesame area dimensions as the individualresistance members. The respective pairs of members are shielded fromeach other by interposed foils 94 of nonmagnetic metal, for examplecopper.

As shown in FIG. 10, the displacing motion of the field plates 17 and 18can be controlled mechanically, such as by the illustrated cam 21.Depending upon the cam cont-our, a desired control or regulatingcharacteristic in dependence upon the angle of cam setting is thusobtained. A spring 22 presses the carrier of the resistance membersproper toward the cam 21, so that each angular position of the camcorresponds to a definite position of the resistance assembly 17, 18relative to the magnetic field.

A potentiometer according to the invention .can further be designed insuch a manner that it need not be actuated mechanically but can becontrolled directly by an electrical magnitude, for example independence upon variation of an electric current. The embodimentillustrated in FIG. 11 affords such a performance. It comprises athree-legged ferromagnetic core structure which has respective fieldgaps in the two outer legs. In the illustrated embodiment the two outerlegs are constituted by two soft-magnetic U-shapal yokes 23 and 24 whichform the above-mentioned air gap between each other and close a splitmagnetic circuit for a permanent magnet 25 which in this exampleconstitutes, or forms part of, the center leg. The outer legs areenergized within the unsaturated and linear range of their magneticcharacteristic by means of two excitation windings 26 and 27 which areshown series connected but may also be connected in parallel relation toeach other.

When the windings 26, 27 are excited, the resulting flux is in boost-ingrelation to the permanent flux at one gap but in bucking relation to thepermanent flux at the other gap. Consequently, now one of the gapsbetween yokes 23 and 24 is traversed by a magnetic flux whichconstitutes the sum of the permanent flux [from magnet 25 and thevariable flux produced by the winding, whereas the field in th other gapconstitutes the difference between the two magnetic fluxes. When nocurrent passes through the windings 26 and 27, the magnetic induction inboth field gaps is the same because it is due only to thepermanentmagnet flux, and the resistance members 28 and 29 located inthe respective gaps have median resistance values. Consequently, whencurrent passes through the windings, the resistance value of the memberlocated in the gap of the higher induction increases, whereas theresistance of the other member now subjected to a lower amount Otfinduction, decreases. The two members are connected in a divider circuitcorresponding to FIG. 2. However, mul tiple divider circuits accordingto FIGS. 3, 5 and 6 are analogously applicable.

An electromagnet can also be used for producing the magnetic field in apotentiometer according to the invention, instead of a permanent magnetas exemplified in the above-described embodiments. When employing anelectromagnet, the division ratio can be further increased by varyingthe excitation of the field-producing magnet in dependence upon theposition ot the galvanomagnetic assembly relative to the direction ofthe magnetic field. If desired, the output voltage of the potentiometercan be made dependent not only upon the positional or otherpotentiometric adjustment mentioned in the foregoing, but can also bevaried in response to another control magnitude. Thus, when employing anelectromagnet for producing the magnetic field, the additional voltagecontrol is readily obtained by varying the excitation current for themagnet coil. For example, when the magnet in FIG. 1 consists of asoft-magnetic core with an excitation coil, an additional control andvariation is afforded by varying the excitation current for that coil;and the same applies to an embodiment 0t the type shown in FIG. 11 itthe permanent magnet 25 is substituted by a soft-magnetic core with anexcitation coil.

To those skilled in the art it will be obvious upon a study of thisdisclosure that my invention permits Olf various modifications and hencecan be given embodiments other than particularly illustrated anddescribed herein, I

without departing from the essential (features of the invention andwithin the scope of the claims annexed hereto.

I claim:

1. A contactless potentiometer, comprising magnetic field structure,voltage supply leads, a voltage divider circuit having twogalvanomagnetic resistance members con nected in series with each otherbetween said leads and having a tap between said two members to providea variable output potential at said tap, said .two resistance membersbeing disposed in the field of said structure to have their respectiveresistances dependent upon the magnetic flux traversing said members andbeing fixed with respect to each other in respectively differentpositions relative to said field structure, and means for simultaneouslycontrolling the amounts of flux through said respective members inmutually inverse relation so that increased flux through one membercoincides with decreased flux in the other.

*2. A contactless potentiometer, comprising magnetic field structurehaving a field gap, a voltage divider circuit having a pair ofgalvanomagnetic resistors connected in series with each other and havingbetween said two mem- 'bers a tap for providing a variable outputvoltage, said two resistance members being disposed in said field gap tohave respective resistances dependent upon the magnetic flux traversingsaid resistors, a carrier structure joining said two resistors to eachother in respectively different positions relative to said gap, one ofsaid structures being displaceable relative to the other for increasingthe flux through one of said resistors while simultaneously decreasingthe flux in the other.

3. A contactless potentiometer according to claim 2, comprising at leaston pair of galvanomagnetic resistors in addition to the [first-mentionedpair, the two resistors of each additional pair being fixedly joinedwith said first pair in said field gap and disposed in respectivelydifferent positions corresponding to those of said first-pair resistors,and the two resistors ot each additional pair being serially connectedwith each other in parallel relation to one of the two resistors of thenext preceding pair.

4. In a contactless potentiometer according to claim 2, said twogalvanomagnetic resistors having respectively diftferent zero-(fieldresistance values.

5. A contactless potentiometer, comprising a magnetic field structurehaving a field gap, a carrier structure in said gap, one Otf said twostructures being angularly displaceatble relative to the other about anaxis transverse to the flux direction, a voltage divider circuit havingtwo galvanomagnetic resistors connected in series with each other andhaving between said two members a tap for providing a variable outputvolt-age, said resistors having substantially flat shape and extendingon said carrier in respective planes parallel to said axis and angularlyrelated to each other so that said angular displacement causes the fluxthrough one resistor to increase while simultaneously decreasing in theother.

6. A contactless potentiometer, comprising a magnetic field structurehaving a field gap, a carrier structure in said gap, said carrierstructure having elongated prismatic shape and a square cross section,one of said two structures being rotatably displaceable relative to theother about an axis transverse to the flux direction in said gap andcoincident with the axis of said prismatic carrier structure, a voltagedivider circuit having a pair of galvanomagnetic resistors of flat shapeconnected in series with each other and mounted on respective mutuallyperpendicular surfaces of said carrier, so that angular displacementcauses the magnetic flux through one resistor to increase whilesimultaneously decreasing in the other resistor of said pair.

7. A contactless potentiometer according to claim 6, comprising at leastone pair of. galvanomagnetic resistors in addition to thefirst-mentioned pair, the two resistors orf each additional pair beingalso mounted on respective mutually perpendicular sunfaces of saidcarrier structure, the two resistors of each additional pair beingserially connected with each other in parallel relation to one of thetwo resistors of the next preceding pair, and the seriesconnectedresistors located on the same one of said carrier surfaces being formedof a single galvanomagnetic resistance member having a plurality oftaps.

:8. in a contactless potentiometer according to claim 7,

the mutually series-connected ones of said resistors on the samesunfiace of said carrier structure being joined together to form asingle integral resistance member having a tap.

9. In a contactless potentiometer according to claim 2, said carrierstructure consisting of electrically conductive material so as to have ashielding eitect.

.-10. In a contactless potentiometer according to claim 2, said carrierstructure consisting of ferromagnetic material [for reducing the activeWidth of said field gap.

11. 'In a contactless potentiometer according to claim 2, said carrierstructure consisting of ferromagnetic material, and cylinder segments offerromagnetic and electrically conductive material mounted on thelateral surtaces of the carrier and covering said resistors, saidsegments supplementing the carrier structure to a substantially circularover-all cross section.

12. In a contactless potentiometer according to claim 2, said fieldstructure having in said gap a field area corresponding in sizesubstantially to the area of one of said two galvanomagnetic resistors,said two resistors consisting of planar plates mechanically joinedbeside each other in a single plane, the direction of relativedisplacement between said two structures being perpendicular to the fluxdirection in said gap.

16. A contactless potentiometer according to claim 12, comprising atleast one additional pair of galvanomagnetic resistors corresponding inarea to the two aforesaid resistors and being mechanically joined withsaid carrier structure, the respective resistors of each additional pairand the respective arfore-said tvv-o resistors being arranged above oneanother.

14. A contactless potentiometer according to claim 12, comprising ametal 'foil between each two pairs Otf said galvanomagnetic resistors.

15. A contactless potentiometer according to claim 12, comprising arotatable drive cam, and translatory transmission means connecting saidcam to said displaceable structure for controlling the voltage divisionin dependence upon the rotational cam position.

16. A contactless potentiometer, comprising a magnetic [field structurehaving a three-legged core Whose two outer legs have respective fieldgaps and whose center leg has magnetic excitation means for passingpre-magnetizing flux through said two gaps, two galvanomagneticresistance members connected in series with each other and disposed insaid respective gaps to have their respective resistances dependent uponthe magnetic flux traversing said members, and a control winding mountedon said structure and inductively linked with both of said outer legs toprovide,

when energized, a control flux bucking said pre-magnetiz-' ing flux inone leg and boosting it in the other, whereby the resultant fluxes insaid resistance members and thus their resistance values are controlledin mutually inverse relation to each other.

17. In a contactless potentiometer according to claim 16, said magneticexcitation means of said center leg being a permanent magnet.

References Cited by the Examiner RICHARD M. WOOD, Primary Examiner.

H. T. POWELL, W. I), BROOKS, Assistant Examiners.

1. A CONTACTLESS POTENTIOMETER, COMPRISING MAGNETIC FIELD STRUCTURE,VOLTAGE SUPPLY LEADS, A VOLTAGE DIVIDER CIRCUIT HAVING TWOGALVANOMAGNETIC RESITANCE MEMBERS CONNECTED IN SERIES WITH EACH OTHERBETWEEN SAID LEADS AND HAVING A TAP BETWEEN SAID TWO MEMBERS TO PROVIDEA VARIABLE OUTPUIT POTENTIAL AT SAID TAP, SAID TWO RESISTANCE MEMBERSBEING DISPOSED IN THE FIELD OF SAID STRUCTURE TO HAVE THEIR RESPECTIVERESISTANCES DEPENDENT UPON THE MAGNETIC FLUX TRAVERSING SAID MEMBERS ANDBEING FIXED WITH RESPECT TO EACH OTHER IN RESPECTIVELY DIFFERENTPOSITIONS RELATIVE TO